Approximately 37,000 people die in the U.S. each year just due to seasonal influenza outbreaks. Efforts to match each year's batch of prevailing influenza viruses fail to predict the strains that will spread in the U.S. 23% of the time. The influenza season of 2007-2008 was one example of the mismatch between prediction and actual strain prevalence. In that season, two of the three influenza strains were mismatched with the viruses that spread in the population leading to influenza infections in vaccinated individuals Therefore, year to year seasonal influenza antigen prediction is not optimal. Beyond seasonal influenza, more troubling is that it is impossible to predict the next pandemic strain of influenza despite our greatest attempts to monitor new out breaks. Even if the strain could be determined at the onset of the pandemic, the time needed to develop and produce an effective vaccine for world-wide distribution may take too long to provide a protective vaccine to the world population. We propose to create and test centralized influenza genes for the production of prophylactic cross-reactive immunity to combat both seasonal and pandemic influenza. Centralized antigens are antigens that have been computationally engineered to represent common or primordial antigen sequences shared by many or all current viral antigen variants. The advantage of using a centralized antigen is that the genetic distance from the vaccine strain to the challenge strain is half of that of a random antigen and a challenge strain. Therefore, unlike selected wildtype candidate antigens, centralized antigens have substantially higher general homology to all strains of influenza, increasing their ability to drive cross-reactive immune responses to control influenza variants. The specific aims of this study are 1) to create reassorted influenza viruses expressing centralized genes. These will include hemagglutinin (HA) and neuraminidase (NA) for H1, H2, H3, H5, N1 and N2 subtypes. The centralized viruses (H1N1-con, H2N2-con, H3N2-con, and H5N1-con) will be used to make traditional inactivated vaccines. 2) In order to determine the most broadly protective vaccine, mice will be immunized with centralized and wildtype inactivated vaccines. The immunized mice will be challenged with divergent influenza viruses and the best vaccine will be determined by the ability to induce the broadest levels of protection. 3) The final goal of the study is to determine the effects of using a centralized influenza vaccine in the context of prior anti-influenza immunity. Vaccine safety is paramount and these studies will determine if boosting with centralized vaccines results in original antigeni sin and dominant non-neutralizing immune responses. A final analysis will be done in ferrets, since ferrets more closely resemble natural influenza infection in humans. The overall goal of this project is to determine if a centralized vaccine is capable of inducing cross-protective immunity against influenza virus with greater breadth than that of a traditional influenza antigen. The most broadly protective antigens, whether centralized or wildtype, could be used as a first line defense or backup vaccine against pandemic or weaponized influenza viruses in the case of vaccine mismatch or could be incorporated into the annual vaccine formulation.